Prof. Dr. Thomas Bohlen
Geophysical Institute
Department of Physics
Karlsruhe Institute of Technology

Dr. Stefan Jetschny
Geophysical Institute
Department of Physics
Karlsruhe Institute of Technology

Sven Heider
Geophysical Institute
Department of Physics
Karlsruhe Institute of Technology

Dr. Ekaterina Rykhlinskaya
Steinbuch Centre for Computing (SCC)
Karlsruhe Institute of Technology

Infrastructure projects worldwide often face the same demands of creating short cuts in order to keep up with the increase in public traffic and transportation. One feasible solution is to go underground. With the increasing number and dimensions of such tunneling projects, the use of tunnel boring machines (TBMs) becomes more prevalent. Tunnel boring machines have the potential for automated and continuous drilling of tunnels with low employment of workers at high performance. Nevertheless, the geologic situation along the tunnel trajectory is less predictable in urban areas due to the limited access for geological probing and geophysical measurements. This can results in uncertainties regarding the actual rock type and the spatial location of structures encountered during the tunnel construction. Sudden changes in the geological and geotechnical properties, i.e., at lithological boundaries, fracture zones or ground water bearing soil can be a serious safety threat to the TBM and usually requires specially designed TBMs. Safely predicting geological structures ahead of the tunnel construction can therefore significantly reduce safety risks and prevent expensive down times of the tunnel boring machine.

We use a parallel 3-D elastic finite difference code in order to simulate the complex elastic wave field in models of arbitrary complexity. With respect to the application in the exploration of the tunnel surrounding we observe similar wave field as shown as in Figure 1. On the basis of a random media model that accounts for small and large scale heterogeneities, typical features encountered in a tunnel construction are included, such as a tunnel tube (white), an excavating damaged zone (contour around the tunnel) and a low dipping lithological boundary (straight contour line). While the tunnel tube is extended, i.e. the tunneling is progressing, we perform several wave field simulation to image the exact position of the dipping structure. Each modeling run takes about 4h on 80 cores. The overall goal is to study the complex wave propagation, optimize the measurement geometry and parameters and finally create synthetic field data to develop new imaging and processing methods. Later on, this gained knowledge is directly applied to field cases.

• Bohlen, T., 2002: Parallel 3-D viscoelastic finite-difference seismic modelling, Computers and Geosciences, 28 (8), 887-899.
• Bohlen, T., U. Lorang, W. Rabbel, G. Müller, R. Giese, S. Lüth, and S. Jetschny, 2007: Rayleigh-to-shear wave conversion at the tunnel face - from 3D-FD modeling to ahead-of-drill exploration: Geophysics, 72, T67–T79.
• Jetschny, S., T, Bohlen and A. Kurzmann,2011:Seismic prediction of geological structures ahead of the tunnel using tunnel surface waves, accepted for publication in Geophysical Prospecting

Area: Geophysics

Software:

• SOFI3D

Links:

• SOFI3D
• Seismic Observation in Underground Development (SOUND)